This application relates to treatment processes and equipment for difficult-to-separate emulsions, and more particularly to treatment of solid-stabilized emulsions.
Most formations bearing hydrocarbons simultaneously produce oil, gas and an aqueous phase, usually brine. Several wells can be tied together through a gathering line into a separation or processing plant, sometimes comprising just a simple tank, where initial gravity separation of water, oil and gas occurs. Water in oil emulsions containing clay and/or silica are common in oil production activities. In oil tankers and refineries, in addition to abundant oil/water emulsion sources, sludge and tank bottoms are also common. Estimates of the volume of emulsion that must be processed are approximately 1 percent of the total worldwide oil production.
Theoretically, gas is taken from the top, water and sediments are drawn from the bottom, and the oil is drawn from the middle of the mixture. However, the mixture can form emulsions which only partially separate by gravity settling and are very difficult or nearly impossible to completely separate by other means. Further, the water stream from the initial separator frequently contains solids and residual emulsified oil making disposal a significant problem, both ecologically and economically. The waste water is often stored in holding ponds where an oily sludge separates out and is recovered for disposal.
Emulsions are generally held together by different interfacial polar and non-polar forces, creating emulsions having a range of stability from low, i.e. relatively easy to separate into oil and water phases, to high or very difficult to separate. The emulsions can be difficult to treat when they contain stabilizing solids such as colloidal silica and clay, particularly nano-clay particles, which are frequently present in producing formations and form an especially stable emulsion, sometimes forming an intermediate emulsion rag layer, which can have a rheology that is highly viscous, gelatinous and/or doughy, usually depending on the temperature. Strong interfacial forces can appear when colloidal disperse-phase particles interact with nano-size clay particles to form the super-stable complex mixture of colloidal liquid droplets and suspended solids in the rag layer.
Breaking emulsions is generally a process of neutralizing the charges between the oil and water interfaces, allowing water and oil droplets to coalesce into larger drops, and to generate two continuous phases to transform the crude oil into a useable anhydrous form for subsequent refinery operations. As used herein, an emulsion is the intimate two-phase mixture of hydrophobic and aqueous phases, with one phase dispersed, as minute globules sometimes called micelles, inside a continuous phase sometimes referred to as the matrix. These micelles are stabilized by an interfacial film, so that the micelles cannot coalesce, and do not respond well to gravity settling. Emulsions where oil micelles are surrounded by water are referred to as oil-in-water emulsions; and where aqueous micelles are surrounded by oil, as water-in-oil or invert emulsions. Both oil-in-water and invert emulsions may be encountered, thus, emulsions could be polar or non-polar depending on the type of force that dominates. Further, the polar forces can be dominated by either cationic or anionic charges, or a dual combination that is sometimes referred as a double layer film or onion skin emulsion. Improper treatment of one type may invert the emulsion to the opposite type.
Oil/water emulsions are normally treated with heat, chemicals and/or centrifuges to separate the oil, water and solids. Heat, steam, frac tanks, chemicals and centrifuges are commonly used in a very energy intensive and costly manner, and moreover can be slow.
U.S. Pat. No. 6,033,448 notes problems caused by gasifying a hydrocarbon stream comprising water and discloses the application of heat and pressure to separate a sludge into a water-lean fuel layer which can be supplied to a gasifier.
U.S. Pat. No. 67,877,027 further heats the sludge by recycling a portion of the hot oil to mix with the sludge, supplying the remaining hot oil to the gasifier.